1. Field of the Invention
The invention relates to a control system for controlling distribution of power from a battery and an engine in a powertrain for a hybrid electric vehicle.
2. Background Art
A powertrain for a hybrid electric vehicle has two sources of power. One source typically is an internal combustion engine, and the second source is a high voltage electric motor, usually an induction motor. One class of hybrid electric vehicle powertrains comprises parallel hybrid electric powertrains.
A parallel hybrid electric powertrain may include two power source configurations, the first configuration comprising a combination of an engine, a motor and a generator with a battery and a planetary gearset for coordinating power distribution. The second power source configuration may comprise an electric drive system with only a motor, a generator and a battery. The battery acts as an energy storing device for the generator and the motor.
The engine output power of the first power source configuration can be split into two power flow paths by controlling the generator speed. A mechanical power flow path is established from the engine to the planetary gear unit, and ultimately to the transmission torque output shaft. The other power flow path is an electrical power flow path that distributes power from the engine to the generator to the motor, and hence to the torque output shaft of the transmission. The generator in this instance can operate also as a power input device, resembling the engine, for distributing power to the gearset if electric drive is desired. With this configuration, the generator, the motor and the gearset may operate as a electro-mechanical transmission with continuously variable ratio characteristics.
By braking the generator, the engine output power can be transmitted with a fixed gear ratio to the torque output shaft of the transmission through a fully mechanical power flow path.
The electric motor of the second power source draws power from the battery and provides driving torque independently of the engine during both forward and reverse drive modes. Further, the generator can draw power from the battery and drive the vehicle forward using a one-way reaction brake on the engine output shaft. In this instance, when the generator drive mode is in operation, the generator acts as a motor.